You're using IE, which means you need to issue the open() before
adding the onreadystatechange handler.
Otherwise, open will trigger a call to your handler, and IE's
implementation won't have reset the readyState to 0.

In either event, you should double-check that the status of the
request is 200 before accessing the result.

 - Godmar

On Nov 29, 2007 9:21 AM, Eric Lease Morgan <[log in to unmask]> wrote:
> Why doesn't my httpRequest Javascript function return unless I add an
> alert? Grrr.
>
> I am writing my first AJAX-y function called add_tag. This is how it
> is suppose to work:
>
>    1. define a username
>    2. create an httpRequest object
>    3. define what it is suppose to happen when it gets a response
>    4. open a connection to the server
>    5. send the request
>
> When the response it is complete is simply echos the username. I know
> the remote CGI script works because the following URL works correctly:
>
>    http://mylibrary.library.nd.edu/demos/tagging/?
> cmd=add_tag&username=fkilgour
>
> My Javascript is below, and it works IF I retain the "alert
> ( 'Grrr!' )" line. Once I take the alert out of the picture I get a
> Javascript error "xmldoc has no properties". Here's my code:
>
>
>    function add_tag() {
>
>     // define username
>     var username  = 'fkilgour';
>
>     // create an httpRequest
>     var httpRequest;
>     if ( window.XMLHttpRequest ) { httpRequest = new XMLHttpRequest(); }
>     else if ( window.ActiveXObject ) { httpRequest = new ActiveXObject
> ( "Microsoft.XMLHTTP" ); }
>
>     // give the httpRequest some characteristics and send it off
>     httpRequest.onreadystatechange = function() {
>
>      if ( httpRequest.readyState == 4 ) {
>
>       var xmldoc = httpRequest.responseXML;
>       var root_node = xmldoc.getElementsByTagName( 'root' ).item( 0 );
>       alert ( root_node.firstChild.data );
>
>      }
>
>     };
>
>     httpRequest.open( 'GET', './index.cgi?cmd=add_tag&username=' +
> username, true );
>     httpRequest.send( '' );
>     alert ( 'Grrr!' );
>
>    }
>
>
> What am I doing wrong? Why do I seem to need a pause at the end of my
> add_tag function? I know the anonymous function -- function() -- is
> getting executed because I can insert other httpRequest.readyState
> checks into the function and they return. Grrr.
>
> --
> Eric Lease Morgan
> University Libraries of Notre Dame
>
> (574) 631-8604
>